Optical and Electrical Spin Injection in Semiconductor Quantum Dots Xavier MARIE Laboratory of Physics and Chemistry of Nano-Objects ; INSA-CNRS 135 avenue de Rangueil, 31077 Toulouse cedex 4, France marie@insa-toulouse.fr The manipulation of carrier spins in semiconductor quantum dots (QD) is an important step towards future spintronic or quantum information processing applications. This approach is attractive since a long coherence time is expected, as a result of the inhibition of classical spin relaxation mechanisms : the discrete energy levels in semiconductor quantum dots and the corresponding lack of energy dispersion lead to a slowdown of the spin relaxation processes compared to bulk or twodimensional structures. We have studied the spin dynamics of electrons, holes, neutral and charged excitons in undoped and doped QD by time-resolved photoluminescence1-6 . We will give a review of our recent experimental results on optical spin injection in InAs/GaAs quantum dots. The possibility of dynamical polarization of nuclei in InAs QD will be also discussed 7-9. Finally we will present results on electrical spin injection in a Spin-LED quantum dots Device 10. 1 Paillard et al., Phys. Rev. Lett. 86, 1634-1637 (2001). Cortez et al, Phys. Rev. Lett. 89, 207401 (2002). 3 Laurent et al., Phys. Rev. Lett. 94, 147401 (2005) 4 Braun et al., Phys. Rev. Lett., 94, 116601 (2005) 5 Senes et al , Phys. Rev. B 71, 115334 (2005) 6 Laurent et al, Phys. Rev. B 73, 235302 (2006) 7 Eble et al , Phys. Rev. B 74, R081306 (2006) 8 Braun et al, Phys. Rev.B 74, 245306 (2006) 9 Lombez et al, Phys. Rev. B 75, 195314 (2007) 10 Lombez et al, App. Phys. Lett, 90, 81111(2007) 2